[react-mui-hooks] `useDataGrid` onPage function return type

## Current behaviour
The `onPage` return type
```ts
{
    rows: GridValidRowModel[];
    totalRowsCount?: number
}
```
is not defined as a type and available to be reused outside the hook.

## Expected behaviour
It would be nice to not have to explicitly know the type declaration and be able to reuse it when defining handlers for the `onPage` property.